Servomotor actuating means



INVENTOR. HAROLD B. SCHULTZ ATTORNEY.

5 Sheets-Sheet 1 Oct. 13, 1964 H. B. SCHULTZ SERVOMOTOR ACTUATING MEANSFiled Aug. 2, 1961 Oct. 13, 1964 H. B. SCHULTZ 3,152,449

SERVOMOTOR ACTUATING MEANS Filed Aug 2, 1961 3 Sheets-Sheet 2 SEE-3INVENTOR. HAROLD B SCHULTZ.

ATToR VE Oct. 13, 1964 H. B. SCHULTZ SERVOMOTOR ACTUATING MEANS 3Sheets-Sheet 3 Filed Aug. 2, 1961 United States Patent 3,152,449SERVUMGTUR ACTUATIING MEANS Harold B. Schultz, South fiend, Ind,assignor to The Bendix Corporation, South Bend, Ind, a corporation ofDelaware Filed Aug. 2, 19:51, Ser. No. 128,720 7 Claims. (Cl. 60-545)The present invention relates to actuating means for servomotors of thetype carrying control structure on its movable power driven elements;and more particularly to actuating structures for the type of servomotordriven hydraulic master cylinders used to power actuate the hydraulicbrakes of automotive vehicles.

The fluid pressure servomotors which are used to power actuate thehydraulic brakes of automotive vehicles generally include a controlvalve structure mounted on the power piston of the servomotorwhichcontrol valve is in turn actuated by means of a foot pedal lever. It isa property of the brake structures of the drum and shoe type, that aconsiderable amount of brake pedal lever movement is required to forcethe shoes out into engagement with the drums, and thereafter only aslight additional amount of foot pedal lever movement is required toproduce the actual braking force. The brake operation therefore may bethought of as occurring in two stages: the first stage of which requiresa large amount of fluid at low pressure to move the shoes intoengagement with the drums; and the second stage of which requires asmall amount of flow at a high pressure to produce the braking force. Inmost systems the transition between the stages occurs at a hydraulicpressure of approximately 100 psi. In general, the servomotor drivenmaster cylinders which are used to actuate these systems discharge fluidto the brake structures in an amount generally proportional to themovement of the controlling foot pedal lever. It has long been desiredby the art to reduce the amount of foot pedal lever travel required toactuate such mechanisms to an amount which generally corresponds withthat required to operate an accelerator pedal of an automotive vehicle.

An object of the present invention is therefore the provision of a newand improved servomotor structure controlled by a manually actuatedmember Whose actuation will occur in two stages: the first of whichproduces a considerable movement of servomotor movement by means of avery small amount of movement of the manually actuated lever; and asecond stage wherein the servomotor movement is generally directlyproportional to the movement of the manually actuated member.

A more particular object of the present invention is the provision of anew and improved fluid pressure servomotor driven master cylinder of anautomotive braking system wherein the shoes of the brake structures areforced out into engagement with their drums by the servomotor withoutrequiring any substantial movement of the manually actuated member; andthereafter the manually actuated control member is caused to have amovement which is substantially directly proportional to the forceapplied between the brake shoes and brake drums.

A still further object of the present invention is the provision of anew and improved actuating mechanism for servomotors which can beinterpositioned between a control structure mounted on the movablemember of the servomotor, and a manually actuated control lever andwherein the connection expands during actuation of the servomotor toreduce the amount of follow-up movement of the servomotors movableelements by the manually actuated control member.

The invention resides in certain constructions and combinations andarrangements of parts; and further objects and advantages will becomeapparent to those skilled in "ice the art to which the invention relatesfrom the following description of several preferred embodimentsdescribed with reference to the accompanying drawings forming a part ofthis specification, and in which:

FIGURE 1 is a schematic view of an automotive braking system in whichits fluid pressure servomotor driven master cylinder and actuatingmechanism is shown in section;

FIGURE 2 is a cross sectional view taken approximately on the line 22 ofFIGURE 1;

FIGURE 3 is a fragmentary cross-sectional View showing anotherembodiment of fluid pressure servomotor and its actuating mechanism; and

FIGURE 4 is a fragmentary enlarged view of the embodiment shown inFIGURE 3.

The automotive braking system shown in FIGURE 1 of the drawingsgenerally comprises a conventional master cylinder A having a fluidpressurizing chamber 10 therein from which hydraulic fluid is forced byreason of the hydraulic piston 12 to the hydraulic motors 14, only oneof which is shown, of a conventional drum and shoe type brake B. Thepiston 12 is adapted to be power driven by means of the movable wall orpower piston 16 of a fluid pressure servomotor C attached to the mastercylinder A. The control valve structure D for the'servomotor C ismounted on and carried by the movable wall 16 of the servomotor; so thatmovement of the control rod 18 of the control valve structure D causesthe movable wall 16 to move correspondingly. The servomotor C shown inthe drawing is of the vacuum submerged type wherein vacuum of the sameintensity is normally communicated to the front and rear power chambers20 and 22 on the front and rear sides respectively, of the movable wall16 during the normal energized condition shown in the drawing.

The control valve D shown in the drawings is of conventionalconstruction and generally comprises a stationary vacuum valve seat 24,a concentric and movable vacuum atmospheric valve seat 26, and anannular poppet member 28 adapted to abut each of the valve seats. Thevalve structure is contained Within an axially extending opening 34which extends through the movable wall 16 and which is provided with arearwardly facing step to provide a rearwardly facing shoulder whichforms the vacuum valve seat 24. The atmospheric valve seat 26 is formedon the rear end of a movable valve control member 32 that is positionedin the opening 30 generally forwardly of the vacuum valve seat 24. Thecontrol rod 18 which is suitably attached to the control member 32 so asto be an operating part thereof controls the movement of the controlmember 32.

The annular poppet member 2% is formed of rubber and includes a frontflange which is molded onto and around a suitable stiffening plate toeffect a suitable seal with respect to both of the valve seats 24 and26. The rear end of the poppet member 28 is provided with an integralflexible diaphragm portion which is suitably secured to the sidewalls ofthe opening 30 to effect a seal therewith. The annular area between thepoppet member 28 and sidewalls of the opening 30 in the region betweenthe vacuum valve seat 24 and the diaphragm portion 34 forms the vacuumchamber 36 of the valve. Vacuum is continually communicated to thevacuum chamber 36 through the vacuum inlet connection 38 to the chamber20 and the vacuum passage 4% in the movable wall 16.

The region of the central opening 36 forwardly of the valve seats 24 and25 forms the control chamber 42 of the valve, and is continuallycommunicated to the rear opposing power chamber 22 by means of theradial passage 44. The central opening 36 extends externally of thehousing of the servomotor through a tubular boss 46 which is suitablysealed with respect to the housing so that atmospheric pressure iscontinually communicated through the central opening in the annularpoppet member 28 to the atmospheric valve seat 26.

The servomotor driven master cylinder structure above described is shownin FIGURE 1 in its normal deactivated condition wherein vacuum of thesame intensity is communicated to both the forward and rearward powerchambers 2G and 22 respectively, and no pressure is being supplied tothe brake applying wheel cylinders 14. When it is desired to actuate thebrakes, the control rod 18 is forced inwardly to cause the poppet member23 to abut the vacuum valve seat 24- and close off vacuum communicationwith the rear opposing power chamber 22. Thereafter a slight furtherforward movement of control rod 18 moves the atmospheric valve seat 26out of engagement with the poppet member 28, thereby causing airpressure to flow through the opening to the rear opposing power chamber22 and force the movable wall 16 forwardly. Movement of the movable wall16 is transmitted through the push rod 59 to the piston 12 causing it toclose off its compensating port 52 and thereafter force fluid to thebrake applying wheel cylinders 14. A block or" rubber 53 is positionedbetween the movable wall 16 and push rod 56 to provide a reaction forceagainst the control member 32 which is generally proportional to theforce applied to the push rod 50. When it is desired to prevent furtherincrease in braking effort, forward movement of the control rod 13 isstopped; whereupon flow of air through the valve continues for a furtherinstant until the movable wall 16 moves forwardly to allow the poppetmember 28 to again engage the atmospheric valve seat 26. Thereafter allflow through the valve structure is stopped and the piston 12 remains ina stationary position. When it is desired to release the brakes, thecontrol rod 18 is allowed to move rearwardly; whereupon the atmosphericvalve seat 26 moves the poppet member 28 out of engagement with thevacuum valve seat 24 to communicate vacuum with the rear opposing powerchamber 22. The resulting decrease in pressure differential across themovable wall 16 permits the hydraulic pressure in the chamber it) plusthe force of the piston return spring 54 to move the movable wall 16rearwardly. The movable wall 16 will stop in any position in which thecontrol rod 18 is held; and if it is desired to completely release thebrakes, the removement of all force from the control rod 18 allows thespring 56 to hold the poppet member 28 out of engagement with the vacuumvalve seat 24, so that the structure again assumes the position shown inthe drawing. The general structure so far described is similar to thatshown and described in the Robert R. Hager application 98,472, nowPatent No. 3,053,235, and for a more complete understanding of itsconstruction and operation reference may be had to that application.

Conventionally, control rod portion 18 of the control member 32 isactuated through mechanical means that is directly connected to the footpedal lever 48 of the automotive vehicle on which it is mounted.Conventionally therefore the movable wall 16 is caused to assume aposition corresponding with the position to which the foot pedal lever48 is moved.

As previously indicated it is an object of the present invention toreduce the amount of pedal lever movement that is required to actuatethe braking systemparticularly during the time that the brake shoes aremoving out of engagement with the brake drum, and during which arelatively large amount of fluid is required to force the shoes intoengagement with the drums. This is accomplished in the embodiment shownin FIGURE 1, by means of an expansible or telescoping member E having ahydraulic chamber 58 positioned between its movable parts for causing anextension thereof. The structure E shown in FIGURE 1 has a body portion60 having a forwardly facing hydraulic chamber 53 therein which isclosed off by means of the hydraulic piston 62. The piston is suitablysealed with respect to the sidewalls of the chamber 58, and the controlrod 18 is suitably fixed to th hydraulic piston 62 so that its movementis controlled thereby. The rear end of the body portion is suitablypinned to the foot pedal lever 48. A suitable guide bearing 64 isinterpositioned between the front end of the body portion 69 and controlrod 18, so that the telescoping member E is suitably supported betweenthe foot pedal lever 48 and the control member 32 to accommodate aslight amount of lateral movement.

Although the expansible member B may be caused to expand at varioustimes during the actuation of the unit to produce various effects, it isshown in FIGURE 1 as being connected to the output of the fluid pressurechamber it) of the master cylinder to receive fluid pressure therefrom.As the servomotor C is actuated therefore, gradually increasing pressurefrom the chamber 16 is communicated to the hydraulic chamber 53 to causeit to expand proportionately so that very little, if any, movement ofthe control foot pedal lever i8 is necessary. It has been chosen in theembodiment shown in FIGURE 1 to terminate the expansion of the member Eat approximately the time that the brake shoes engage the brake drums.This occurs when the pressure in the discharge of the master cylinder Areaches a pressure of approximately 100 p.s.i.; by reason of a valvestructure F which closes off communication between the master cylinderand the expansible chamber 58 at this time. The valve structure F canbest be seen in FIGURE 2 of the drawings, and as shown, is formed in thebody section 66 by means of a transverse passage or bore 66 beneath theexpansi'olc chamber 58. The bore 66 is provided with an outwardly facingshoulder 63 against which a ball valve 7% is adapted to seat and toshut-off fiow from the master cylinder to the expansible chamber 58.Flow from the master cylinder enters the open end of the bore 66, and asmall passageway 72 inwardly of the shoulders 68 communi cates this flowto the expansible chamber 53. A coil spring 74 is provided to bias theball toward the valve seat 68, and the ball '79 is normally held out ofengagement with the valve seat 68 by means of a hydraulic piston 76 thatis positioned inwardly of the valve seat 68. A coil spring '73 biasesthe piston '76 to a position which holds the ball 79 out of engagementwith the valve seat 68. The coil spring 78 works through a washer 80which abuts a shoulder 82 on the piston member 76, and valve openingmovement is limited by abutment of the Washer 89 with another shoulder34 in the opening 66. The spring 78 is normally compressed by an amountwhich holds the piston 76 in its valve opening position until a pressureof approximately p.s.i. is asserted against the piston; whereupon theforce of spring 73 is overcome and the piston moves to allow the ball 72to abut the valve seat 63. Thereafter further expansion of thetelescoping member E is prevented, and the foot pedal lever 48 moves inaccord with the power member 16. inasmuch as this occurs after the timethat the brake shoes have engaged the brake drum, there is thereafterprovided a movement of the foot pedal lever 4-8 which is indicative ofthe amount of braking effort being produced.

The embodiment of brake actuating system shown in FIGURE 3 of thedrawings corresponds generally with that shown in FIGURE 1, and differsprincipally therefrom in the arrangement of expansible member E which 1sused to actuate the control rod 13'. The structure shown in FIGURE 3 isintended to actuate a master cylinder A which is identical with thatshown in FIGURE 1; and those portions of IGURE 3 which are similar tocorresponding portions in FIGURE 1 are designated by like numeral orletter, characterized further in that a prime mark is affixed thereto.

The expansible structure E is a hydraulic equivalent of the generalstructure E shown in FIGURE 1 in that motion from the pedal lever 48 istransmitted to the control rod 18 by means or" hydraulic displacement.The structure shown in FIGURE 3 generally comprises a conventionalmaster cylinder 86, which may be identical to the master cylinder Ashown in FIGURE 1, and which is actuated by means of the foot pedallever 48, In general the structure E includes an expansible chamber 58'which is expanded during the initial stage of brake actuation withoutusing any of the displacement from the master cylinder 86, until suchtime as the brake shoes engage the drums. Thereafter displacement fromthe master cylinder 36 is valved to the expansible chamber 58 so thatmovement of the foot pedal lever 48 then occurs in a manner proportionalto the amount of braking effort which is achieved. The structure Egenerally comprises a cast housing 88the forward portion of which issuitably fixed as by snap rings 91 to the movable wall structure 16 ofthe fluid pressure motor C, and the rear portion of which is providedwith an axially extending cylinder bore forming the expansible chamber58'. A piston 92 closes oif the rear end of the expansible chamber 58,and the piston 92 is held stationary by means of a bracket 94 whichextends between the piston 92 and the shell of the servomotor structureC. It will therefore be seen that movement of the power piston 16'causes an expansion of the expansible hydraulic chamber 58.

The forward end of the cast housing 83 is also provided with an axiallyextending valve actuating bore 96 of substantially the same size as isthe bore 53. The bore 96 is closed off by means of a piston 98 which isshown at an integral part of the control rod 18. Discharge from themaster cylinder 86 is continually communicated to the valve actuatingbore 96, so that pressure upon piston 93 causes an actuation of theservomotor C which is directly proportional to the pressure generated inthe master cylinder 86.

The structure shown in FIGURE 3 further includes a valve structure F forcontrolling communication between the expansible chamber 53 and the lowpressure reservoir 1% of the master cylinder 86. In the embodiment shownin FIGURE 3, communication is permitted up until such time as thepressure generated in the master cylinder 86 causes a pressure to beproduced in the outlet of master cylinder A, not shown, of approximately100 psi. At this time, the valve structure F is actuated to close offcommunication between the reservoir 1% and expansible chamber 53, andcommunicates the discharge of the master cylinder 86 to the expansiblechamber 5'8 to provide a follow-up movement of the foot pedal lever 48.

The valve structure F is formed in the housing $8 by means of a verticalbore 1% having an outlet port in its inner end which communicatesdirectly to the expansible chamber 58. Adjacent the inner end of thevertical bore Hi2 there is provided a pressure inlet passage 106 whichcommunicates pressure from the master cylinder 86 to the outlet passage1194. The outlet passage 1634 is adapted to be closed off by means of aneedle type poppet 108 which is yieldably carried by a piston 110 in thebore 162. The needle type poppet 108 has a cylindrical head 112 thereonwhich is slidingly received within a bore 114 in the bottom end of thepiston 110. Downward movement of the piston 110 is limited by means ofengagement of flange 11s on the piston 110 with a shoulder 118, and thepiston is normally held in this position by means of a coil spring 126.A predetermined sealing force is provided for the poppet 1% by a coilspring 122 positioned between the poppet 103 and the bottom of the bore114 and separation of the needlepoppet 1198 from the piston 110 isprevented by suitable snap ring means in the bore 114 beneath thecylindrical head 112 of the poppet 108.

The upper end of the piston 110 is provided with a tubular projectingportion 124, and the outer end of the bore 102 is closed oh" by a cap126 having a bore 128 which slidingly receives the outer end of thetubular projection 124-, and which bore 128 is always communicated tothe expansible chamber 58'. The space 130 between the cap 126 and pistonis always communicated with the reservoir 1% by means of line 131. Adrilled passage 132 through the tubular projection 124 is provided forcommunicating chamber 131 with the central opening 133 through thetubular projection 124. The cap member 126 further includes a steppedbore 134 communicating with bore 123 and having needle type poppet 135therein which is yieldably biased into chamber 128 to a position spacedfrom the end of the tubular projection 124 when the flange 116 engagesthe shoulder 118. Upward movement of the tubular portion 124 causes itto abut the end of the needle poppet 135 to close off flow through thetubular projection 124. The portion of the bore 123 in the cap member126 into which the tubular member 124 projects is communicated by meansof a passage 136 to bore 134 and its passage 137 in the cast housing 88leading to the expansible chamber 58.

During the normal de-energized condition of the sys tem therefore, thepiston 111D engages the shoulder 118, passage 11% is closed off by thepoppet 1%, and the poppet 135 is out of engagement with the tubularprojection 124 to permit flow of fluid from the reservoir 1% to theexpansible chamber 58. Depressing of the foot pedal lever 48 builds uppressure within the master cylinder 36 which causes the piston 98 tomove the control rod 18 and hence actuate the servomotor C to forcefluid out of its actuated master cylinder A, not shown. Movement of themovable wall 16 of the servomotor C causes the housing 88 to move alongwith it; and inasmuch as the piston 92 is held stationary with respectto the housing of the servomotor C by means of a suitable bracket 94,the expansible chamber 58 is caused to enlarge. Inasmuch as the poppet135 is out of engagement with the tubular portion 124, low pressurefluid from the reservoir 1% is free to enter the expansible chamber 58as it is expanded by the movable wall 16. The only displacementtherefore which is used from the master cylinder 86 during this initialstage of actuation, is that required to actuate the control valvestructure D, and therefore substantially no movement of the foot pedallever 48 takes place.

After a predetermined pressure has been developed by the master cylinder86, the spring yields to allow the piston 11%) to move upwardly tosequentially close off the passage 137 through the tubular projection124 from the expansi'ole chamber 55, and thereafter left the poppet 1118out of sealing engagement with the seat surrounding passage 194, tocommunicate fluid discharge from the master cylinder 86 to theexpansible chamber 58. Thereafter any further actuation of the footpedal lever 48 causes displacement of the master cylinder 86 to be usedto enlarge the expansible chamber 58 so that there would be a movementof the foot pedal lever 48 generally corresponding to that of themovable wall 16 of the servomotor C. In the preferred embodiment shownin the drawing, the spring 121 is preloaded to yield when the pressurefrom the master cylinder 86 produces a suflicient actuation of theservomotor C to cause the shoes of the vehicles brakes to engage theirbrake drums.

It will be apparent that the valve structure F can be modified to causedifferent arrangements of follow-up movement of the movable wall 1% bythe foot pedal lever 48. Where for example, the valve structure F ismade to communicate with the master cylinder 86 to the expansiblechamber 58 normally, and at a predetermined pressure close oficommunication between the expansible chamber 5% and the master cylinder86, and in turn communicate it with the reservoir 1%; foot pedal levermovement would be provided initially, and would thereafter be preventedfrom exceeding a predetermined value. This arrangement can be used toprovide brake operation at the time that the brake pedal lever wouldnormally be bottomed out against the floor boards of the vehicle.

It will be apparent that the objects heretofore enumerated, as well asothers, have been accomplished, and that there has been provided anactuating system for a servomotor of the follow-up type which preventsfollowup movement of the manually actuated lever during certain periodsof actuation.

While the invention has been described in considerable detail, I do notwish to be limited to the particular construction shown and described;and it is my intention to cover hereby all novel adaptations,modifications and arrangements thereof which come within the practice ofthose skilled in the art to which the invention relates.

I claim:

1. In a servomotor driven hydraulic pressure developing system having apower driven movable structure on which the control member for theservomotor is mounted in such manner that movement of said controlmember in one direction causes said power driven structure to move insaid direction and thereby cause said control member to follow theactuating movement of said power driven movable structure, saidservomotor producing a reaction force on said control member in anopposite direction which is generally proportional to the forcedeveloped by its movable structure in said one direction, and saidsystem including hydraulic pressurizing means which produces a hydraulicpressure generally proportional to the force which said servomotordevelops: telescoping mcans having an internal variable volume chamberseparating two expandable portions, a reaction means spaced from saidcontrol member, one portion of said telescoping means being operativelyconnected to said control member, and the other portion of saidtelescoping means being operatively connected to said reaction means andmeans communicating said hydraulic pressure of said hydraulicpressurizing means to said variable volume chamber to expand saidportions during actuation of said servomotor and thereby permit therelative positions of said control member and said servomotor to changeduring actuation of said system.

2. In a servomotor driven hydraulic pressure developing system having apower driven movable structure on which the control member for theservomotor is mounted in such manner that movement of said controlmember in one direction causes said power driven structure to move insaid direction and thereby cause said control member to follow theactuating movement of said power driven movable structure, saidservomotor producing a reaction force on said control member in anopposite direction which is generally proportional to the forcedeveloped by its movable structure in said one direction, and saidsystem including hydraulic pressurizing means which produces a hydraulicpressure generally proportional to the force which said servomotordevelops: a telescoping means having an internal variable volume chamberseparating two expandable portions, a reaction means spaced from saidcontrol member, one portion of said telescoping means being operativelyconnected to said control member, and the other portion of saidtelescoping means being operatively connected to said reaction means,means communicating said hydraulic pressure of said hydraulicpressurizing means to said variable volume chamher to expand saidportions during actuation of said servomotor and thereby permit therelative positions of said control member and said servomotor to changeduring actuation of said system, and a regulating valve in said lastmentioned means for regulating the flow of hydraulic fluid to saidvariable volume chamber.

3. In an actuating system for a servomotor having a power driven movablestructure on which the control member for the servomotor is mounted insuch manner that movement of said control member in one direction causessaid power driven structure to move in said direction and thereby causethe control member to follow the actuating movement of said power drivenstructure: a manually actuated member, telescopic means operatively L5interpositioned between said manually actuated member and said controlmember for transmitting actuating force from said manually actuatedmember to said control member, said means having two telescopic partsforming an expansible hydraulic chamber which makes said meansexpandable, a collapsible hydraulic pressurizing chamber collapsed bysaid power driven structure to force hydraulic fluid therefrom, and flowcommunicating means communicating said collapsible chamber to saidexpandable chamber as said servomotor is actuated to decrease travel ofsaid manually actuated member.

4. In an actuating system for a servomotor having a power driven movablestructure on which the control member for the servomotor is mounted insuch manner that movement of said control member in one direction causessaid power driven structure to move in said direction and thereby causethe control member to follow the actuating movement of said power drivenstructure: a manually actuated member, telescopic means operativelyinterpositioned between said manually actuated member and said controlmember for transmitting actuating force from said manually actuatedmember to said control member, said means having telescopic partsforming an cxpansible hydraulic chamber which makes said meansexpandable, a coilapsible hydraulic pressurizing chamber collapsed bysaid power driven structure to force hydraulic fluid therefrom, flowcommunicating means for communicating said collapsible chamber to saidexpandable chamber as said servomotor is actuated, and valve means forclosing off said flow communicating means, said valve means being closedwhen the pressure generated in said collapsible chamber reaches apredetermined value.

5. In a servomotor including hydraulic pressurizing means according toclaim 1 and further comprising a valve means for restricting flowthrough said means communicating hydraulic pressure to said variablevolume chamber in accordance with a force applied to said control memberto prevent failure of said telescoping means.

6. In a fluid pressure servomotor and the like:

a housing having an internal axially extending chamber therein;

a movable wall in said chamber, said movable wall having a generallycylindrically shaped boss axially extending through one end of saidhousing, said boss having an axially extending internal valve chambertherein which is stepped down in at least two successive stages toprovide inner and outer shoulders facing axially outwardly of said valvechamber;

an annular flexible poppet member having an inner thickened portion forengaging said inner shoulder,

an outer portion having an interference fit with the side walls of saidvalve chamber, and an integral flexible portion interconnecting saidinner and outer portions;

a control member positioned axially inwardly of said poppet member andhaving an axially outwardly facing valve seat for engaging said poppetmember radially inwardly of said inner shoulder and adapted for axialmovement to sealingly engage said poppet member and disengage it fromsaid inner shoulder;

a control rod connected to said control member and projecting axiallyoutwardly through said annular poppet member;

a pivotally mounted foot pedal lever; and

a telescoping member operatively connecting said foot pedal lever tosaid control rod with a variable volume chamber interposed therebetween.

7. In a fluid pressure servomotor and the like according to claim 6 andfurther comprising:

a block of elastomeric material having an outer face seated against saidinner shoulder;

a force transmitting member slidably mounted in an Mag opening in saidmovable Wall and positioned adjacent an inner face of said block ofelastomeric material;

a hydraulic pressurizing means operatively connected to said forcetransmitting member; and 5 mit the relative positions of said foot pedallever 10 2,924,072

and said control rod to change during actuation of said system.

References Cited in the file of this patent UNITED STATES PATENTSStelzer Mar. 10, 1942 Elliott Apr. 27, 1948 Rockwell Oct. 10, 1950Porter Aug. 19, 1958 Burwell Feb. 9, 1960 UNITED STATES PATENT OFFICECERTIFICATE OF CORRECTION Patent N0. 3 152 449 October l3 1964 Harold B,Schultz It is hereby certified that error appears in the above numberedpatent requiring correction and that the said Letters Patent should readas corrected below.

Column 6, line 46 for "left" read lift line 65 strike out "with".

Signed and sealed this 6th day of April 1965,

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner ofPatents

6. IN A FLUID PRESSURE SERVOMOTOR AND THE LIKE: A HOUSING HAVING ANINTERNAL AXIALLY EXTENDING CHAMBER THEREIN; A MOVABLE WALL IN SAIDCHAMBER, SAID MOVABLE WALL HAVING A GENERALLY CYLINDRICALLY SHAPED BOSSAXIALLY EXTENDING THROUGH ONE END OF SAID HOUSING, SAID BOSS HAVING ANAXIALLY EXTENDING INTERNAL VALVE CHAMBER THEREIN WHICH IS STEPPED DOWNIN AT LEAST TWO SUCCESSIVE STAGES TO PROVIDE INNER AND OUTER SHOULDERSFACING AXIALLY OUTWARDLY OF SAID VALVE CHAMBER; AN ANNULAR FLEXIBLEPOPPET MEMBER HAVING AN INNER THICKENED PORTION FOR ENGAGING SAID INNERSHOULDER, AN OUTER PORTION HAVING AN INTERFERENCE FIT WITH THE SIDEWALLS OF SAID VALVE CHAMBER, AND AN INTEGRAL FLEXIBLE PORTIONINTERCONNECTING SAID INNER AND OUTER PORTIONS; A CONTROL MEMBERPOSITIONED AXIALLY INWARDLY OF SAID POPPET MEMBER AND HAVING AN AXIALLYOUTWARDLY FACING VALVE SEAT FOR ENGAGING SAID POPPET MEMBER RADIALLYINWARDLY OF SAID INNER SHOULDER AND ADAPTED